Control circuits



April 22, 1952 E. C. HARTWIG CONTROL CIRCUITS Filed Jan. 18, 1946 WITNESSES:

ATTORNE Patented Apr. 22, 1952 CONTROL CIRCUITS Edward C. Hartwig, Pittsburgh, Pa, assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application January 18, 1946, Serial No. 642,041

Claims. (Cl. 25027) This invention relates to an electronic control circuit and has particular relation to a control circuit for controlling the supply of current from a source of alternating voltage to a load such as a resistance welding load.

In certain resistance welding apparatus constructed in accordance with the teachings of the prior art, a welding transformer is supplied with current from an alternating voltage supply source through a pair of inversely connected electric valves of the arc-like type, such as ignitrons; Various circuits are provided to render the ignitrons conductive alternately in opposite half-periods of the supply voltage throughout a predetermined time interval with the instant at which an ignitron is rendered conductive in a half-period being selectable to determine the heat produced at the weld. Such prior apparatus on the whole operates satisfactorily, but it has a limited range of selection of the instant in a half-period at which an ignitron is rendered conductive and does not permit an ignitron to become conductive at the instant corresponding to a zero supply voltage.

However, a wide range of selection is many times desirable; and when a series capacitor is employed in the load circuit to correct the power factor so that the voltage on the capacitor at the instant of zero supply voltage makes positive the anode of the ignitron to be next conductive, it is particularly desirable to render the :ignitron conductive at that instant.

It is accordingly an object of my invention to provide a new and improved control circuit for controlling the supply of current from an alternating voltage source to a load.

Another object of my invention is to provide a new and improved control apparatus for use instant in a half-period of the supply voltage.

A further object of my. invention isto provide a novel control apparatus for controlling the supply of current from an alternating voltage source to a load through a pair of inversely connected electric valves in which the instant in a half-period at which a valve becomes conductive is selectable over a wide range including the instant corresponding to zero supply voltage.

In accordance with my invention, a wide range of selection of the instant in a half-pe riod at which a main valve becomes conductive is permissible through the provision of a time delay of one half-period between the timing control and the actual control of the main valves.

The features of my invention which I consider novel are set forth with greater particularity in of the apparatus comprises a pair of main elec- Welding transformer H.

tric valves '3 and 5 of the arc-like type, preferably ignitrons, connected inversely with each other and in series with a capacitor 1 and the primary winding 9 of a welding transformer II between a pair of supply lines l3 and I5 energized from an alternating voltage source IT. A pair of welding electrodes I9 and 2| and the material 23 to be welded are connected in series across the secondary winding 25 of the The capacitor 1 in series with the primary winding 9 of the welding transformer H, is employed to correct the power factor but may be omitted if desired.

An electric discharge valve 21 of thearc-like type, preferably a thyratron, is connected between the anode 29 and the ignition electrode 3! of the first main valve 3 through a current limiting resistor .33. A similar valve is connected between the anode 37 and ignition electrode 39 of the second main valve 5 through a current limiting resistor 4t. These two valves 21 and 35 are hereinafter referred to as firing valves.

The control circuit of the firing valve 21 for the first main valve 3 extends from the control grid 43 thereof through a grid resistor'45, a resistor 41 in parallel with a secondary winding 49 of a first firing transformer 51 and a biasing resistor 53'to the cathode 55. A biasing voltage is impressed across the biasing resistor 53 by a suitable means usch as a rectified current supply circuit 57 energized from the alternating voltage supply lines. The. biasing voltage on the biasing resistor 53 tends tomaintain the first firing valve 2'! non-conductive so that it becomes conductive only when a voltage sufficient to overcome the biasing voltage is impressed in the control circuit through the first firing transformer 5|. When the first firing valve 21 becomes conductive, a current flows through that valve and the ignition electrode 3| of the corresponding first main valve 3 to render the main valve conductive.

A similar control circuit for the second firing valve 35 extends from the control grid 59 to the cathode 6| thereof and includes a grid resistor 63, a secondary winding 65 of a second firing transformer 61 in parallel with a resistor 62, and a biasing resistor II havin a biasing voltage supplied thereacross through a suitable rectifier circuit l3 energized from the supply lines. When the second firing valve 35 conducts, current fiows through the ignition electrode 39 of the second main valve 5 to render that main valve conductive.

The supply of voltage impulses through the firing transformers 5| and 6'! to cause the main valves to become conductive is controlled by an intermediate circuit l5 which in turn is controlled by a timing circuit TI and a heat control circuit 19.

The intermediate circuit I5 includes a first capacitor 8| corresponding to the first main valve 3 and. a second capacitor83 corresponding to the second main valve 5. The primary winding 85 of the first firing transformer 5| is connected in series with an auxiliary electric valve 81 across the first capacitor 8| to form a discharge circuit 9;:

therefor. This auxiliary valve 81 is preferably of the arc-like type, such as a thyratron, and is hereinafter referred to as the first discharging valve.

The primary winding 85 of, the second firing transformer 57 is connected in series with another auxiliary valve SI across the second capacitor 83 to form a discharge circuit therefore This auxiliary valve BI is also preferably of the arclike type, such as a thyratron, and is hereinafter s and I5. A capacitor I09 is connected across the biasing resistor 99 to smooth out the voltage ripple.

The biasing voltage on resistor 99 tends to maintain the first discharging valve 81 non-conductive so that it may be rendered conductive only by a voltage overcoming the biasing voltage which may be impressed across the resistor 91 in the control circuit through another auxiliary transformer II I, the secondary winding II3 of which is connected across the resistor 91. The auxiliary transformer III is a part of the heat control circuit Is to be described hereinafter.

The control circuit of the second discharging valve 9| is similar to that of the first discharging valve 81 and extends from the control grid II5 to the cathode Ill and includes a grid resistor I I9, another resistor I2I in parallel with a second secondary Winding I23 of the auxiliary transformer I I I in the heat control circuit, and a biasing resistor I25. across the biasing resistor I25 from another auxiliary supply transformer I21 through a rectifier I25 with a capacitor I3I in parallel with the resistor I25 to smooth out the voltage ripple.

A bias- I It is then evident that when a discharging valve is rendered conductive to discharge the correspending one of the capacitors ill and 83 through the primary winding of the corresponding firing transformer, a voltage impulse is supplied in the control circuit of the corresponding firing valve to cause the corresponding main valve to become conductive.

A charging circuit is provided for each of the capacitors 8| and 85 which is energized by the voltage appearing across the right hand portion of the secondary winding I 55 of the auxiliary transformer I01. The charging circuit for the first capacitor 8| extends from the right hand end of the secondary winding I55 through a resistor I33, a control capacitor I35, another electric valve IBI and the first capacitor 8| to the intermediate tap I39 on the secondary winding I55. This last-mentioned valve I3? is of the arclike type, preferably a thyratron, and is hereinafter referred to as the first charging valve. This valve I3! is controlled by the timing circuit ll.

The charging circuit for the second capacitor 83 extends from the intermediate tap I39 of the secondary winding I55 through the second capacitor 83, a conductor I li, another electric valve Hi3 of the arc-like type, such as a thyratron, hereinafter referred to as the'second charging valve, the control capacitor I35 and the resistor i33 to the right hand end of the secondary winding IE5. It is therefore obvious that the first charging valve I3? may conduct current to charge the first capacitor 8| only in half-periods of the supply voltage of one polarity while"the second charging valve Hi3 may conduct current to charge the second capacitor 83 only in half-periods of the opposite polarity. The arrangement is such that the first capacitor 8| may be charged only in a half-period of a polarity opposite to that in which the corresponding first main valve 3 may conduct current. Similarly. the second capacitor 83 may be charged only in a half-period of opposite polarity to that in which the second main valve 5 may be conductive.

While the first charging valve I3? is controlled directly by the timing circuit ii, the second charging valve i 53 is controlled by what is known as a follow-up circuit. The control circuit for the second charging valve I43 extends from the control grid i 35 thereof through a grid resistor A biasing voltage is supplied Ml, a biasing resistor I59, and the control capacitor I35 to the cathode I5I. A biasing voltage exists across the biasing resistor I49 tending to maintain the second charging valve I43 nonconductive. However, when the first charging valve I3! conducts current to charge the first capacitor 8|, that current also charges the control capacitor I35. The voltage across the charged control capacitor I35 opposes the biasing voltage across the resistor I49 and causes the second charging valve I43 to become conductive in the next half-period of the supply voltage when its anode I53 becomes positive. Thus every time the first charging valve I31 becomes conductive, the second charging valve M3 is rendered conductive in the next succeeding half-period.

The timing circuit l? which controls the first charging valve is similar to that shown in the copending application of Stadum and Freeman, Serial No. 642,042, filed January 18, 1946. The timing circuit includes an output resistor I55 through which current flows in each half-period of the alternatingsupply voltage of one polarity throughout a predetermined time interval followrent.

ing operation of a starting switch I51. The details of the operation of the timing circuit may be found in the aforesaid copending application of Stadum and Freeman.

An intermediate tap I59 on the output resistor I55 is connected through a biasing resistor -I6I and a grid resistor I63 to the control electrode I65 of the first charging valve I 31 while the cathode I61 thereof is connected to the lower end of the output resistor through conductor I69.

A biasing voltage tending to maintain the first charging valve I31 non-conductive appears across the resistor I63 and is opposed by the voltage created across output resistor I55 by the flow of current therethrough. The arrangement is such that the current flows through theoutput resistor I55 in the half-periods in whichthe first charging valve I31 may conduct. Thus, the first charging valve I31 is rendered conductive in each half-period in which the corresponding main valve 3 cannot conduct throughout a predetermined time interval.

The heat control circuit 19 which controlsthe operation of thedischarging valves 81 and 9| is shown and described in my copending application, Serial No. 642,040 filed January 18, 1946, now

Patent No. 2,504,834. The heat control circuit is efiective upon closure of a hand switch I1I to produce a voltage impulse in each of the secondary windings H3 and I23 of an output transin a half -period of the supply voltage in which the corresponding main valve may conduct our- As explained in my copending application the voltage impulses may be supplied at a time corresponding to zero supply voltage.

In operating the apparatus, the hand switch I'1I in the heat control circuit 19 is first closed.

As a result, voltage impulses are impressed in the control circuits of the discharging valves 81 and 9| tending to render them conductive alternately in successive half-periods. However,

since the capacitors 8| and 83 are not charged, the discharging valves do not then become conductive.

The starting switch I51 in the timing circuit 11 is then closed causing the first charging valve I31 to be rendered conductive in each half-period in which main valve 3 cannot conduct to effect charging of the first capacitor 8|.

' which each is charged by virtue of the pulses supplied from the heat control circuit 19 which render the discharging valves 81 and 9| conductive. Because of the inductance of the primary windings 85 and 83 in the discharge circuits of capacitors BI and 83, each of the discharging valves 81 and SI becomes non-conductive before the corresponding charging valve I31 or I43 again becomes conductive. As each capacitor BI and 83 is discharged, a voltage impulse is impressed in the control circuit of the corresponding firing valve to render it conductive, which in turn, renders the corresponding main valve conductive. I

This operation continues with the main valves 3 and 5 being rendered conductive alternatelyin opposite half-periods at a preselected instant in such half-period until after the expiration of the preselected time interval at which time the first charging valve is prevented from becoming conductive and charging of the capacitors 8| and 83 is halted. It is apparent that the main valves 3 and 5 are rendered conductive once more after the last charging of the capacitor 8I through the first charging valve so that the actual control of the main valves is delayed by oneihalfperiod of the supply voltage behind the operation of the timing circuit itself. This enables theheat control circuitto effectthe discharging of the capacitors BI and 83 and consequently the rendering conductive of the main valves 3 and 5 at any selected instant in a corresponding halfperiod including that at which the supply voltage is substantially zero.

Although I have shown and described a particular heat control circuit, it is obvious that various other suitable circuits may be employed to supply the desired impulses in the control circuits of the discharging valves. Likewise, other timing circuits may be employed to time the operation of the charging valves although that disclosed is particularly suitable in connection with the specific intermediate circuit here shown.

Although I have shown and described a specific embodiment of my invention, I am aware that many other modifications may be made without departing from the spirit of the invention. I do not intend therefore to limit my invention to the particular embodiment disclosed.

I claim as my invention:

1. Control apparatus for supplying current from a source of alternating voltage to a load, comprising a pair of electric valves of the arelike type to be connected in circuit with said source and load to control thesupply of current, said valves being connected inversely whereby they may be conductive in half-periods of said source voltage of opposite polarity; a pair of capacitors corresponding individually to different ones of said valves; means including timing apparatus adapted to conduct during alternate halfperiods of said sources when performing a timing operation and in so conducting causing each or" said capacitors to be charged in each half-period of said source voltage of opposite polarity to that in which the corresponding valve may conduct throughout a preselected time interval; adjustable timing means connected to each capacitor for discharging that capacitor at a preselected instant in each half-period in which the corresponding valve may conduct, said preselected instant being determinable at the will of the operator; means connected to each valve and responsive to the discharge of the corresponding capacitor for rendering the valve conductive; and means for maintaining each said valves non-conductive regardless of the polarity of its anode-cathode potential until rendered conductive by the discharge of its corresponding capacitor.

2. Control apparatus for supplying current from a source of alternating voltage to a load, comprising a 'pair of electric valves of the arelike type to be connected in circuit with said source and load to control the supply of current, said valves being connected inversely whereby they may be conductive in half-periods of said source voltage of opposite polarity, and said load being of the type capable of introducing a shift in the phase of the potential impressed on said valves relative to the potential of said source, such that the anode-cathode potential of one of said valves may at times be positive at instants when said source potential is substantially Zero; a pair of capacitors corresponding individually to different ones of said valves; means including timing apparatus adapted to conduct during alternate half-periods of said sources when performing a timing operation and in so conducting causing each of said capacitors to be charged in each half-period of said source voltage of opposite polarity to that in which the corresponding valve may conduct throughout a preselected time interval; means connected to each capacitor for discharging that capacitor at a preselected instant in each half-period in which the corresponding valve may conduct, said preselected in-= stant being determinable at the will of the operator; means connected to each valve and responsive to the discharge of the corresponding capacitor for rendering the valve conductive; and means iior maintaining .each said valves non-conductive regardless of the polarity of its anode-cathode potential until rendered conductive by the discharge of its corresponding capacitor. l

3. Control apparatus for supplying current from a source of alternating voltage to a load, comprising a pair of main electric valves of the arc-like type to'be connected in circuit with said source and load to control the supply of current, said main valves being connected inversely whereby they may be conductive in half-periods of said source voltage of opposite polarity; a pair of capacitors corresponding individually to diilerent ones of said main valves; means including timing apparatus adapted to conduct during alternate half-periods of said sources when performing a timing operation and. in so conducting causing each of said capacitors to be charged in each halfperiod of said source voltage of opposite polarity to that in which the corresponding main valve may conduct throughout a preselected time interval; a discharge circuit including an auxiliary valve connected across each capacitor; control means connected to each auxiliary valve for causing it to become conductive to effect rapid discharge of the corresponding capacitor at a preselected instant in each half-period in which the corresponding main valve may conduct, said preselected instant being determined at the will of the operator; means connected to each main valve and responsive to the discharge of the corre- .sponding capacitor for rendering the main valve conductive; and means for maintaining each said main valves non-conductive regardless of the polarity of its anode-cathode potential until rendered conductive by the discharge of its corresponding capacitor.

4. Control apparatus for supplying current from a source of alternating voltage to a load, comprising a pair of electric valves of the arclike type to be connected in circuit with said source and load to control the supply of current, said valves being connected inversely whereby they may be conductive in half-periods of said source voltage of opposite polarity; a pair of capacitors corresponding individually to different ones of said valves; timing means for producing a predetermined control voltage during alternate half-periods of said source voltage of one polarity throughout a preselected time interval; means responsive to said control voltage for causing each of said capacitors to be charged in each half-period of said source voltage of- Opposite polarity to that in which the corresponding valve may conduct; a normally incomplete discharge circuit connected across each of said capacitors; means for completing each discharge circuit individually at a preselected instant in each halfperiod in which the corresponding valve may conduct, said preselected instant being determined at the will of the operator; means connected to each valve and responsive to the discharge of the corresponding capacitor for rendering the valve conductive; and means for maintaining each said valves non-conductive regardless of the polarity of its anode-cathode potential until rendered conductive by the dissaid load including a highly inductive component and a-power factor correcting capacitor, and said load being of the type which is supplied with current during intermittent short intervals of the order of several half-periods of said supply; comprising a pair of electric valves of the arclike type to be connected in circuit with said source and load to control the supply of current, said valves being connected inversely whereby they may be conductive in half-periods of said source voltage of opposite polarity; a pair of capacitors corresponding individually to different ones of said valves; timing means for producing a predetermined control voltage during alternate half-periods of said source voltage of one polarity throughout a preselected time interval; means responsive to said control voltage for causing each of said capacitors to be charged in each half-period of said source voltage of opposite polarity to that in which the corresponding valve may conduct; a normally incompletedischarge circuit connected across each of said capacitors; means for completing each discharge circuit individually at a preselected instant in each halfperiod in which the corresponding valve. may conduct, said preselected instant being determined at the will of the operator; means connected to each valve and responsive to the discharge of the corresponding capacitor for rendering the valve conductive; and means for maintaining each said valves non-conductive regardless of the polarity of its anode-cathode potential until rendered conductive by the discharge of its corresponding capacitor.

6. Control apparatus for supplying current from a source of alternating voltage to a load. comprising a pair of main electric valves of the arc-like type to be connected in circuit with said 7 source and load to control the supply of current,

' pair of capacitors corresponding individually to different ones of said main valves, a charging circuit connected to each capacitor and includ-' voltage of opposite polarity to that in which the corresponding main valve may conduct throughout a preselected time interval; means connected to each capacitor for discharging that capacitor at a preselected instant ineach halt-period in which the corresponding main valve may conduct, said preselected instant being determined at the will of the operator; means connected to each main valve and responsive to the discharge of the corresponding capacitor for rendering the main valve conductive; and means for maintaining each said valves non-conductive regardless of the polarity of its anode-cathode potential until rendered conductive by the discharge of its corresponding capacitor.

7. Control apparatus for supplying current from a source of alternating voltage to a load, comprising a pair of main electric valves of the arc-like type to be connected in circuit with said source and load to control the supply of current, said main valves being connected inversely whereby they may be conductive in half-periods of saidsource voltage of opposite polarity; a pair of capacitors corresponding individually to different ones of said main valves; a charging circuit connected to each capacitor and including an auxiliary source of current and a first auxiliary valve; a timing circuit adapted to conduct during alternate half-periods of said sources when performing a timing operation and in so conducting effective to cause the first auxiliary Valve to be conductive to charge the corresponding capacitor in each half-period of said source voltage of opposite polarity to that in which the corresponding main valve may conduct throughbecome conductive to eiiect rapid discharge of the corresponding capacitor at a preselected instant in each half-period in which the corresponding main valve may conduct, said preselected instant being determined at the will of the operator; means cbnnected to each main valve and responsive to the discharge of the corresponding capacitor for rendering the main valve conductive; and means for maintaining each said valves non-conductive regardless of the polarity of its anode-cathode potential until rendered conductive by the discharge of its corresponding capacitor.

8. Control apparatus for supplying current from a source of alternating voltage to a load, comprising a pair of electric valves of the arclike type to be connected in circuit with said source and load to control the supply of current, said valves being connected inversely whereby they may be conductive in half-periods of said source voltage of opposite polarity; a pair of capacitors corresponding individually to diiierent ones of said valves; means including timing apparatus adapted to conduct during alternate half-periods of said sources when performing a timing operation and in so conducting causing each of said capacitors to be charged in each half-period of said source voltage of opposite polarity to that in which the corresponding valve may conduct throughout a preselected time interval; means connected to each capacitor for discharging that capacitor at a preselected instant in each half-period in which the corresponding valve may conduct, said preselected instant being determinable at the will of the operator and occurring at any instant throughout said half-period; means connected to each valve and responsive to the discharge of the corresponding capacitor for rendering the valve conductive; and means for maintaining each said valves non-conductive regardless of the polarity of its anode-cathode potential until rendered conductive by the discharge of its corresponding capacitor.

9. In combination, terminals for supplying potential; a first thyratron having an anode and a cathode, a capacitor connected in series with said anode and cathode and said terminals; a second thyratron having an anode, a cathode and a grid; a first circuit including in series said lastnamed anode, said last-named cathode, said ca- Dacitor and said terminals; and a second circuit including in series said grid, said last-named cathode and said capacitor; said anode of said first thyratron and said cathode of said second thyratron being connected to one plate of said capacitor.

10. In combination a capacitor; a first thyratron having an anode and a cathode; terminals for supplying a potential; a second thyratron including an anode, a cathode and a grid; a circuit for charging said capacitor to one polarity including in series said anode and said cathode of said first thyratron, said capacitor and said terminals; a circuit for discharging said capacitor and recharging it to the opposite polarity including in series said anode of said second thyratron, said cathode of said second thyratron and said capacitor, and connections between said capacitor and said gridand said cathode of said second thyratron connecting the plate of said capacitor which is negative when said capacitor is recharged to said grid and the other plate to said cathode of said second thyratron.

EDWARD C. HARTWIG.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,289,321 Collom July 7. 1942 2,428,592 Stadum Oct. 7, 1947 

